Fluid loss control in oil field cements

ABSTRACT

A cement fluid-loss composition and its use in a well cementing process are disclosed. The cement fluid loss composition comprises an aqueous slurry of about 35 to about 90 weight percent of water based on weight percent of dry cement; and about 0.1 to about 2 weight percent of a terpolymer based on weight percent of dry cement, said terpolymer having the formula: ##STR1## wherein x is about 40 to about 98 mole %, more preferably about 50 to about 95 mole %, and most preferably about 80 to about 90, y is about 1 to about 50 mole %, more preferably about 2 to about 20 mole %, and most preferably about 5 to about 10 mole %, and z is about 1 to about 50 mole %, more preferably about 2 to about 20, and most preferably about 5 to about 10, y is equal to z, B is about 1 to about 50 mole %, more preferably about 2 to about 20 mole %, and most preferably about 5 to about 10 mole %, wherein B, y and z are less than 60 mole %.

This is a division of application Ser. No. 651,897 9-19-84, now U.S.Pat. No. 4,626,285.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to materials which reduce the filtrationof fluid into permeable earth formations during cementing processes inthe drilling and completing of subterranean wells, particularly wellsfor the recovery of petroleum resources.

Petroleum well cementing is the process of mixing a slurry of cement,water, and other additives and pumping it down through steel casing tocritical points in the oil well annulus around the casing or in the openhole below the casing string. The primary functions of the cementingprocess are to restrict fluid movement between geological formations andto bond and support the casing. In addition the cement aids inprotecting the casing from corrosion, preventing blowouts by quicklysealing formations, protecting the casing from shock loads in drillingdeeper wells, and sealing off lost circulation or thief zones.

A common problem in petroleum well cementing is the flow of liquid fromthe cement slurry into porous earth formations in contact with thecement. This fluid loss is undesirable since it can result indehydration of the cement slurry, and it causes thick filter cakes ofcement solids which can plug the well bore. The fluid lost can damagesensitive formations. Cement fluid loss is particularly a problem in theprocess known as squeeze cementing.

There is a requirement, therefore, for materials which, when added tothe cement formulation, reduce the loss of fluid from the slurry toporous formations.

2. Description of the Prior Art

A type of fluid loss agent used in oil well cementing consists of amedium molecular weight grade of hydroxyethylcellulose (HEC) which maybe employed with or without a dispersant such as condensednapthalenesulfonic acid salts. There are several disadvantages to theuse of hydroxyethylcellulose as a cement fluid loss control agent,however, among which are that it causes undesirable viscosification andretardation of the cement and that it loses effectiveness in thepresence of soluble calcium salts and at elevated temperatures.

Another cement additive employed for control of fluid loss is acopolymer of acrylamide and acrylic acid [L. F. McKenzie, F. M.McElflesh, SPE 1-623,279 (1982)]. Although this material performs wellat high temperature and in the presence of soluble calcium salts, it hasthe undesirable property of strongly retarding cement. This retardingeffect increases with increasing temperature, most likely due to thehydrolysis of the unstable amide groups contained in the polymer whichaccelerates at elevated temperature. Hydrolysis of amide functionsproduces additional carboxylic acid residues which are credited withcement retarding activity.

Still other materials utilized for the control of fluid loss during wellcementing are combinations of polyamines and either lignosulfonate orcondensed naphthalenesulfonic acid salts [L. F. McKenzie, J. V. Eckerts,and P. M. McElfresh, Oil and Gas J. 80 (13) 146 (1982)]. These additivesare valuable since they cause little viscosification of the cement, andthey have little sensitivity to dissolved calcium and moderately hightemperatures. The utility of the polyamine-sulfonate combination issomewhat limited, however, by two side effects they produce: retardationand settlement (free water) of the cement.

Mixtures of HEC, polyvinyl pyrrolidone and sodium naphthalenesulfonatehave been reported as cement fluid loss additives (Wersend, U.S. Pat.No. 3,132,693 (1964) as have mixtures of poly(vinylpyrrolidone) andsodium naphthalenesulfonate-formaldehyde condensation products (U.S.Pat. No. 3,359,225).

Also complex mixtures of maleic anhydrideN-vinylpyrrolidone copolymerswith polymers of poly (aryl-vinylbenzyl) alkyl- and hydroalkylsubstituted quaternary ammonium bases and salts have been used (Wahl,U.S. Pat. No. 3,140,269 (1964)).

An improved fluid loss additive for well cements consists of 30 to 70weight percent of N-vinylpyrrolidone homopolymer, from about 5 to 19weight percent of carboxylmethylhydroxyethylcellulose, and the sodiumsalt of condensed naphthalenesulfonic acid. [B. W. Hale, U.S. Pat. No.4,258,790 Mar. 31, 1982)].

Copolymers of N-vinylpyrrolidone and metal salts of styrenesulfonic acid(1) are known, but only as components in oil containing microcapsulesused in films. [K. Saeki, H. Matsukawa, U.S. Pat. No. 3,855,146 (1974)].

Despite the art for the control of cement fluid loss which is alreadyknown, there exists a need for novel agents capable of improving fluidloss control which are not reduced in utility by the limitationsdescribed above.

SUMMARY OF THE INVENTION

Accordingly, the present invention teaches the preparation ofterpolymers of acrylamide (AM), methacrylamidopropyltrimethyl ammoniumchloride (MAPTAC), and metal neutralized styrenesulfonic acid (SSS) andthe use of these terpolymers as agents for the control of fluid loss topermeable earth formations from formulations for the cementing ofsubterranean wells, particularly wells from which are produced naturalpetroleum resources.

The present invention discloses cementing formulations which comprise:(a) water; (b) a hydraulic cement; (c) from 0.05 to 5.0 wt % based onthe weight of the dry cement of a terpolymer of acrylamide,methacrylamidopropyltrimethyl ammonium chloride, and a metal salt ofstyrenesulfonate, said terpolymer ranging in composition from 40 to 98mole % and in reduced viscosity in 2% NaCl at 0.5 wt % from 0.5 to 15dl/g, and (d) optionally other such cement additives as may be requiredto achieve the desired cementing results.

In addition, the present invention relates to a family of intramolecularpolymeric complexes (i.e. polyampholytes) which are terpolymers ofacrylamide/metal styrenesulfonate/methacrylamidopropyltrimethylammoniumchloride (MAPTAC) and to the use of the polyampholytes as agents for thecontrol of fluid loss to permeable earth formations from formulationsused for cementing subterranean wells, particularly those wells fromwhich natural petroleum resources are produced.

The water-soluble terpolymers of this invention are terpolymers ofacrylamide/sodium styrenesulfonate/methacrylamidopropyltrimethylammonium chloride. These polymersare prepared by free radical polymerization in aqueous solution at40°-60° C. Typical free radical initiators for the polymerization areagoisobutyronitrile (AIBN), potassium persulfate and the like.

The present invention relates to improved process for cementing pipe ina gas or oil well which comprises a terpolymer having the formula:##STR2## wherein x is about 40 to about 98 mole %, more preferably about50 to about 95 mole %, and most preferably about 80 to about 90, y isabout 1 to about 50 mole %, more preferably about 2 to about 20 mole %,and most preferably about 5 to about 10 mole %, and z is about 1 toabout 50 mole %, more preferably about 5 to about 10, y is equal to z, Ais about 1 to about 50 mole %, more preferably 2 to about 20 mole %, andmost preferably about 5 to 10 mole %, wherein A, y and z are less than60 mole % and M is an amine or a metal cation selected from the groupconsisting of aluminum, iron, lead, Groups IA, IIA, IB and IIB of thePeriodic Table of Elements.

Several other polymer compositions were synthesized along the identicalsynthetic route. The composition of these polymers are shown in thefollowing formulae: (Note: These possess an excess of the cationicmonomer - MAPTAC). ##STR3## wherein x is about 40 to about 98 mole %,more preferably about 50 to about 95 mole %, and most preferably about80 to about 90, y is about 1 to about 50 mole %, more preferably about 2to about 20 mole %, and most preferably about 5 to about 10 mole %, andz is about 1 to about 50 mole %, more preferably about 2 to about 20,and most preferably about 5 to about 10, y is equal to z, B is about 1to about 50 mole %, more preferably about 2 to about 20 mole %, and mostpreferably about 5 to about 10 mole %, wherein B, y and z are less than60 mole %.

It should be pointed out that neither the mode of polymerization(solution, suspension, or emulsion polymerization technique and thelike), nor the initiator is critical, provided that the method or theproducts of the initiation step does not inhibit production of thepolyampholyte or chemically modify the initial molecular structure ofreacting monomers.

Typically water soluble monomers incorporated into the terpolymers thatare envisioned in the present invention are listed as follows:

Anionic: 2-acrylamido-2-methylpropane sulfonic acid, sodium styrenesulfonate, (meth)acrylic acid, 2-sulfoethylmethacrylate, and the like.

Cationic: methacrylamidopropyltrimethylammonium chloride,dimethyldiallylammonium chloride,2-methacryloxy-2-ethyltrimethylammonium chloride,trimethylmethacryloxyethylammonium methosulfate,2-acrylamide-2-methylpropyltrimethylammonium chloride,vinylbenzyltrimethylammonium chloride, and the like.

Nonionic: (N,N-dimethyl)acrylamide, hydroxyethyl (meth)acrylate, alkylsubstituted acrylamide, (meth)-acrylates, N-vinyllactanes (e.g.,n-vinyl-2-pyrrolidone), and the like.

GENERAL DESCRIPTION OF THE INVENTION

The present invention relates to the preparation of terpolymers ofacrylamide, methacrylamidopropyltrimethylammonium chloride, and metalsalts of styrenesulfonic acid and to the use of the terpolymers asagents for the control of fluid loss to permeable earth formations fromformulations used for cementing subterranean wells, particularly thosewells from which natural petroleum resources are produced.

The terpolymers of this invention are terpolymers of acrylamide,methacrylamidopropyltrimethylammonium chloride, and metal salts ofstyrenesulfonic acid. These terpolymers are prepared by free radicalcopolymerization in aqueous solution at 40°-60° C. Typical free radicalinitiators for the polymerization are azoisobutyronitrile (AIBN),potassium peroxydisulfate, and the like. The terpolymers consist of from40 to 98 mole % of N-vinylpyrrolidone and 1-50 mole % of a salt ofstyrenesulfonic acid. Preferred for their better performance as cementfluid loss control agents are the copolymers consisting of 50-95 mole %of N-vinylpyrrolidone and 2-20 mole % styrenesulfonic acid salt.

The cation of the styrenesulfonic acid salt may be any cation whichprovides a water soluble salt in combination with the styrenesulfonateanion and which causes no undesirable effects in the cementingformulation such as excessive cement acceleration, retardation, freewater, thickening or thinning, etc. Some cations which providestyrenesulfonic acid salts suitable for use in these terpolymers arelithium, potassium, sodium, triethylammonium, tri(hydroxyethyl) ammoniumand the like. These cations represent typical examples of appropriatespecies, but a wide range of cations may be properly used, and thelisting of typical cations is in no way intended to limit the scope ofthe invention.

The terpolymers found useful as agents for the control of cement fluidloss are further characterized by the viscosity which they impact toaqueous solutions. The viscosity parameter chosen to describe theterpolymers of this invention is the so-called reduced viscosity ofsolutions consisting of 2% by weight sodium chloride, 0.5% by weightpolymer, and the remainder water. The terpolymers ofacrylamide/methylacrylamidopropyltrimethylammonium chloride andstyrenesulfonic acid salts which are disclosed as part of the subjectinvention are those having a reduced viscosity of from 0.5 to 15 dl/g.

This invention also discloses a means for controlling the fluid loss topermeable earth formations from formulations used in the cementing ofsubterranean wells, particularly those wells drilled for the productionof oil and gas by use of the terpolymers discussed above andsubsequently detailed in Examples 1 through 6. The amount of theterpolymer utilized in a cement formulation will vary with theparticular borehole environment at hand. Geological formationcharacteristics, borehole properties, borehole depth, contaminants,temperatures and pressures encountered, cement type and other additives,and purpose and method of application of the cementing operation willinfluence the determination of quantities of the terpolymers of thisinvention to be used in a particular cement formulation to achieve thedesired effect. In addition the particular properties of the terpolymerwill influence the determination of quantities to be used. Because ofthese factors, it is impossible to specifically state nominal usagelevels under all environments or conditions. Those skilled in the art ofsubterranean well cementing will be able to easily determine neededquantities of the terpolymers for cement fluid loss control by testingformation characteristics, formation temperatures and pressures, andcement formulation characteristics, and by otherwise assessing the fluidloss characteristics required of the cement formulation. Nevertheless,it can be stated that a treatment rate of 0.1% to 2% (by weight based ondry cement weight) of the terpolymer should be appropriate. It ispossible that under some circumstances as little as 0.05% or as much as5% of the terpolymer would be required.

The oil well cements employed in the instant invention are APIclassification cements - A, B, C, D, E, F, G, and H, pozzolanic cements,pozzolan-line cements, resin or plastic cements, gypsum cements, dieseloil cements, expanding cements such as API classification cements K, andM, calcium aluminate cements, and latex cements.

The terpolymers prepared and used according to this invention may beadded to the cement slurry in a variety of ways. They may be applied ina solid form either being premixed with the cement before it is added towater or the solid polymers may be added to the cement water slurry.Alternatively, the terpolymers may be applied as aqueous solutions tothe dry cement or cement slurry. In the latter cases the water includedin the terpolymer solution replaces an equal amount of water normallyincluded in the cement slurry.

The amounts of water and cement contained in the subject cementingcompositions which include the terpolymers of AM/SSS/MAPTAC are highlydependent on the type of cement being used, the other additives beingused in the cementing formulation, the borehole conditions and thetechniques being used to apply the cement formulation to the borehole.Those skilled in the art of borehole cementing will by consideration ofthese factors be able to determine the proper cement slurry formulationwhich will maximize benefits from inclusion of the terpolymers of thisinvention.

A variety of other additives may be used in a cement formulation treatedwith the terpolymers of this invention. For example, cement hardeningretarders, hardening accelerators, materials to lower or raise thedensity of the slurry, lost-circulation-control agents, frictionreducers, stabilizers for high temperature strength, etc. may all beused together with this polymer. This list of formulation ingredientswhich might accompany the polymer of this invention in a cement slurryis meant to be exemplary, but in no way are the accompanying materialslimited to those mentioned herein. These and other cement additives maybe combined with the subject terpolymer as it is determined appropriateby workers skilled in the well cementing art.

The terpolymers, cement formulations, and processes described herein asembodiments of the subject invention represent substantial improvementsto the art of subterranean well cementing. As compared to the materialsand methods known previously for the control of fluid loss in wellcementing formulations, use of the subject terpolymers is advantageousin several respects. Unlike many of the previously known compositions,the terpolymers described herein are fully active fluid loss controlagents alone. They have remarkable thermal stability and provideexcellent fluid loss control at temperatures greater than 200° F.without many of the undesirable side effects common to other cementfluid loss control agents. The subject terpolymers cause littlethickening of the cement slurry, little retardation of the cementthickening and no increase in free water. Thus, these materialsrepresent a broadly applicable, general purpose cement fluid losscontrol treatment, of the type needed for the difficult cementingenvironments more and more commonly encountered in today's well drillingsituations.

DETAILED DESCRIPTION OF THE INVENTION

The following examples will further illustrate the novel qualities ofthe additive compositions and processes of the present invention withoutin any way limiting the scope of this invention.

EXAMPLE 1

Synthesis

A representative example for the synthesis of the terpolymer materials(designated 136A) is outlined below.

Into a 1-liter, 4-necked flask add:

12.08 g methacrylamidopropyltrimethylammonium chloride (MAPTAC), 50%aqueous solution;

5.64 g sodium styrene sulfonate (SSS)

35.0 g acrylamide (AM)

300 ml distilled water

or on a molar basis:

5.0 moles MAPTAC

5.0 moles SSS

90.0 moles AM

We should emphasize that the anionic and cationic monomers were added tothe aqueous phase without attempting to form ion-pair comonomers that donot possess nonpolymerizable counterions.

The solution was purged with nitrogen gas for approximately one hour toremove dissolved oxygen. As the nitrogen gas purging began, the solutionis heated to 50° C. At this point, 0.1 g potassium persulfate (i.e.,initiator) was added to the solution. After 8 hours, the polymer wasprecipitated from solution with acetone. Subsequently, the resultingpolymer was washed several times with a large excess of acetone anddried in a vacuum oven at 60° C. for 24 hours. The composition of 136Ais as follows:

    x=0.90

    Y+Z=0.082

    A=0.018

Note that the polymer structure has 1.8 mole % "excess" nonpolymerizablefree charge attached to some of the styrene sulfonate units.

EXAMPLE 2

A further representative example for the synthesis of an intramolecularpolymer complex (designated 136B) is similar to Example 1, except forthe initial monomer feed composition. This is outlined below:

34.6 g methacrylamidopropyltrimethylammonium chloride, 50% aqueoussolution

5.76 g sodium styrene sulfonate

35.0 g acrylamide

or on a molar basis

5.0 moles MAPTAC

7.0 moles SSS

88.0 moles AM

The composition of 136B is as follows:

    x=0.887

    Y+Z=0.087

    B=0.026

Note that the polymer structure has 2.6 mole % "excess" nonpolymerizablefree charge attached to some of the MAPTAC units.

EXAMPLE 3

A further representative example for the synthesis of an intramolecularpolymer complex (designated 136C) is similar to Example 1, except forthe initial monomer feed composition. This is outlined below.

45.5 g methacrylamidopropyltrimethylammonium chloride, 50% aqueoussolution

5.9 g sodium styrene sulfonate

35.0 g acrylamide

or on a molar basis

5.0 moles MAPTAC

9.0 moles SSS

86.0 moles AM

The composition of 136C is as follows:

    x=0.871

    Y+Z=0.901

    B=0.038

Again, it should be noted that the polymer structure has 3.8 mole %"excess" nonpolymerizable free charge attached to some of the MAPTACunits.

136A is best described as an intrapolymer complex with a modest amountof anionic charge, while 136B and 136C terpolymers contain increasingamounts of cationic charge.

As is well known to those versed in the art, the level of ionic monomersincorporated in the growing polymer chain is directly related to theinitial concentration of the reacting species. Therefore, modulation ofthe ionic charge within the polymer structure is accomplished throughchanges in the initial anionic and/or cationic vinylic monomerconcentrations.

EXAMPLE 4

Tests were performed to show the ability of the subject terpolymers tocontrol fluid loss from cement slurries.

In those cases where complete dehydration of the cement occurred beforethe 30 minute test period had expired the fluid loss was extrapolated to30 minutes using the relationship

    FL.sub.30 =FL.sub.T (30)/T

where

FL₃₀ =extrapolated 30 min. fluid loss in ml

FLT=fluid loss for time T in ml

T=duration of test until complete cement slurry dehydration in min

The fluid loss values obtained in this way are denoted by an asterisk(*).

The test results given in Table 1 demonstrate the significant control ofcement fluid loss afforded by polymers of this invention.

                  TABLE 1                                                         ______________________________________                                        Description            Fluid loss ml/30 min.                                  ______________________________________                                        polyacrylamide ampholyte terpolymer-                                                                 30                                                     136A                                                                          acrylamide/acrylic acid copolymer                                                                    84                                                     (90 mole %/10 mole %) respectively                                            neat cement            +3000 ml                                               ______________________________________                                    

EXAMPLE 5

A test was performed to show the lack of effect of the terpolymers ofthis invention upon the tendency of solid material to settle from cementslurries containing them (free water content). Each cement slurry wasprepared as described in Example 4. After the 20 min. paddle stirredaging period, the slurry was again mixed for 35 sec. at high speed in aWaring Blender. The slurry was then used to fill a 250 ml graduatedglass cylinder having a graduated length of 240 mm. After the cylinderstood quiescent for 2 hours the supernatant water was measured. Thisprocedure is similar to but slightly simpler than that described in APISpecification 10, Appendix K.

The results recorded in Table 2 attest to the lack of effect on cementslurry free water exerted by the terpolymers described here.

                  TABLE 2                                                         ______________________________________                                        Polymer Sample No.                                                                             Free Water, ml                                               ______________________________________                                        None             2                                                            136A             nil                                                          90/10 AM/AA      nil                                                          ______________________________________                                    

What is claimed is:
 1. A process for cementing pipe or casing on a gasor oil well which penetrates a formation which comprises depositing inthe space between said pipe or said casing and said formation an aqueousslurry comprising:(a) about 35 to about 90 weight percent of water basedon weight percent of dry cement; and (b) about 0.1 to about 2 weightpercent of a terpolymer, based on weight percent of dry cement saidterpolymer having the formula: ##STR4## wherein x is about 40 to about98 mole %, y is about 1 to about 50 mole %, z is about 1 to about 50mole %, y is equal to z, a is about 1 to about 50 mole %, wherein B, yand z are less than 60 mole %.
 2. A method according to claim 1 whereinM is sodium.
 3. A method according to claim 1 wherein said terpolymerpossesses a nonstoichiometric amount of anionic groups.
 4. A methodaccording to claim 1 wherein said water has about 0.01 to about 10 gramsof salt of acid per 100 ml of said water.